"Dormant" secondary metal-alkyl complexes are not omnipresent

Area of Science:

• Catalysis
• Polymer Chemistry
• Theoretical Chemistry

Background:

• The phenomenon of "dormancy" in propylene polymerization, where active sites lose activity after a 2,1-insertion regioerror, is debated.
• Existing catalytic systems show varied responses to this dormancy, with consensus on its occurrence lacking in some cases.

Purpose of the Study:

• To theoretically investigate the "dormancy" of active sites in propylene polymerization.
• To explain why some catalytic systems do not exhibit dormancy despite regioerror events.
• To explore the factors influencing catalytic activity and reactivity in polymerization.

Main Methods:

• Density-functional theory (DFT) calculations were employed.
• Two distinct homogeneous catalytic systems were modeled: an octahedral C2-symmetric system and a bridged indenyl catalyst.
• Extensive models incorporating counteranion and solvent effects were developed.

Main Results:

• DFT calculations demonstrate that both primary and secondary alkyl complexes can exhibit equal reactivity in propylene polymerization.
• The study explains the lack of intuitive dormancy in certain catalytic systems.
• Calculations on a classical second-generation Ziegler-Natta system supplement the findings.

Conclusions:

• The concept of "dormancy" in propylene polymerization is not universally applicable across all catalytic systems.
• Catalyst structure, counteranion, and solvent effects play crucial roles in determining active site reactivity.
• Theoretical modeling provides insights into complex catalytic behaviors, challenging established assumptions.